Carburetor metering system alone and in combination with a wick or spark plug

ABSTRACT

A carburetor metering system is provided comprising a fuel valve including a valve member movable with respect to a valve seat to vary the fuel flow, the valve member and the valve seat having substantially parallel inclined surfaces and which define therebetween a passage for the flow of fuel having a width corresponding to the distance apart of the surfaces and a length. A wick for use a carburetor metering system is also provided for absorbing liquid for vaporization into an air flow, comprising a cloth of woven strands and means for suspending said cloth in the air flow. There is also provided a spark plug for use in a fuel combustion system. A carburetor metering system is also provided, comprising air flow control valve for metering the flow of air in dependence upon the air pressure differential across the air flow control valve and to maintain the pressure differential at a predetermined value, a fuel valve being operatively connected to said air flow control valve means so that the fuel valve provides a respective increase and decrease in fuel flow rate in respective dependence upon air flow rate and a fuel pressure differential valve for maintaining the pressure differential across the fuel valve.

This application is a divisional of U.S. Ser. No. 08/056,372, filed Apr.30, 1993, now U.S. Pat. No. 5,384,074, which is in turn is a divisionalof U.S. Ser. No. 07/404,839, filed Sep. 8, 1989, now U.S. Pat. No.5,207,207.

BACKGROUND OF THE INVENTION

This invention relates to carburetor metering systems for supplying afuel/air mixture either alone or in combination with a wick or sparkplug.

Automotive engines rarely operate at full power, so the part loadcondition is of greatest importance. This requires accurate metering ofthe fuel over a very wide range of flow rates. It has been said that theonly reason a conventional carburetor can survive is because engines arevery tolerant of rich mixture. Thus the conventional system, whichcannot provide accurate metering over a wide flow rate range, isdesigned to provide richer than ideal mixture at operating points--suchas low load--when it is not accurate. This approach is not adequate fortoday's conditions when emissions and fuel economy are subject tolegislative control.

It is known that substantial advantages are to be obtained, in terms ofpart load fuel economy and decrease of exhaust pollution, by operating aspark ignition engine with a fuel/air mixture having excess air overthat required for just complete combustion of the fuel, that is with alean mixture of fuel in air. As mixture is weakened carbon monoxideemission rate falls rapidly to a low level and then remains low. NOxproduction is a maximum for air fuel ratios of about 17:1 (14.7:1 ischemically correct) after which it falls progressively. Unburnedhydrocarbons fall progressively as mixture is weakened, down to aminimum after which they increase. This increase is caused either byvery slow burning leading to flame extinction before completion or byoccasional misfiring. Experiments show that improved ignition can hastenthe whole combustion process to a degree and so postpone the increase ofthe leaner mixture. Improved ignition also minimizes the risk ofmisfire.

Conventional engines can readily tolerate excess fuel in the fuel/airmixture to a considerable degree. However, lean mixture operationrequires precise control of mixture strength to ensure reliableoperation without misfiring. Thus conventional carburetor systems aregenerally unsuitable for supplying engines operating at lean mixturestrengths.

A carburetor system suitable for supplying lean mixtures of fuel in airis disclosed in British Patent Specification No. 1,595,315. Thiscarburetor-comprises an evaporator for evaporating the fuel into astream of air and a closed-loop control arrangement for maintaining themixture strength at a required value in dependence on the temperaturedrop measured across the evaporator. While such a carburetor is capableof operating adequately in a lean burn system, it has a fairly slowresponse time, typically of the order of 1/4 second, which can renderthe engine sluggish in operation. It would therefore be advangageous toprovide a carburetor metering system which provides accurate fuel/airmixtures, particularly lean mixtures, and adjusts the mixture quickly independence on load changes over a wide range of air flows.

The present invention is also directed to an improved wick for avaporizer usable in a carburetor metering system. One such wickvaporizer is disclosed in U.S. Pat. No. 4,290,401, in the name of thepresent applicant, and which is incorporated by reference herein. Such awick vaporizor comprises a plurality of suspended wick elements havingbottom ends of unequal length suspended above a liquid fuel reservoir,with the number of wicks that are wet at any one time being dependent onthe level of fuel in the reservoir. Temperature measuring means areprovided in an air stream both before and after the air stream passesthrough the vaporizer. The amount of measured temperature drop of theair stream across the vaporizer indicates the latent heat of the liquidfuel and thus the amount of liquid fuel being introduced into the airstream by evaporation. The level of fuel in the reservoir is adjusted ina controlled fashion in response to the temperature drop. This wickvaporizor arrangement provides good closed loop control. However animproved wick construction which provides an improved vaporization ratewould be desireable.

The present invention also relates to a spark plug for use in acombustion system. A conventional spark plug has a body, within which issupported an insulated central electrode and on which a side electrodeis secured so as to extend over the end of the central electrode.Conventionally the central and side electrodes have respective opposingflat surfaces, across which the spark is generated, the distance apartof these surfaces being adjusted by bending the side electrode towardsor away from the central electrode. The two generally flat surfaces arethus often set at an arbitrary angle so that one portion of the pair ofsurfaces is closer together than another. The point or points at whichthe spark will occur is thus quite random.

Sparking, therefore, often occurs in a zone which is relatively enclosedbetween the electrodes and to which only a small amount of combustiblemixture may have penetrated. Flame generation may thus, in some cases berelatively slow. This may give rise to incomplete combustion or poorcombustion characteristics, in relation to the travel of the piston, orotherwise. Erosion of the electrodes due to uneven sparking, or sparkingin one particular zone is also observable.

The time cycle is of course short but it has been shown that there aretwo stages of combustion, namely spark initiation, during which there isno pressure rise, and then general flame propogation across thecombustion chamber. The boundary between the two stages is indistinctbut can be defined as the point in time at which the pressure firstdeparts detectably from the level it would have if no combustion tookplace. The duration of the first stage is known to depend on thepressure and temperature of the charge just before the spark and also onthe mixture strength in and around the spark gap, but not, to any greatextent, on turbulence in the combustion chamber. The duration of thesecond stage depends again on pressure, temperature and mixture strengthbut also very strongly on turbulence. Engines are usually timed so that,at a usual working speed, the first stage and about half of the secondstage are completed by the time the piston reaches top dead center. Anysignificant variation from this timing results in loss of efficiency.

It is also well known that fuel economy and improved exhaust pollutionare improved if the mixture is as lean as possible. The shorter thefirst stage, the more practical is the use of leaner mixtures.

When conventional sparking plugs are used, the duration of the firststage of ignition increases greatly as mixture strength is reduced.

For example, in the publication, "The High Speed Internal CombustionEngine", by Sir Harry Ricardo published 1953 (4th edition), results oftests are given as follows:

    ______________________________________                                                          Angle turned by                                             Mixture strength  crank during first                                          (% chemically correct)                                                                          stage                                                       ______________________________________                                         70               50°                                                   80               20°                                                   90               10°                                                  100                6°                                                  110                5°                                                  120                5°                                                  ______________________________________                                    

(These results were taken at an engine speed of 2000 rpm.) Increasedspark advance reduces the pressure and temperature at time of the spark.As mixture is weakened or engine speed is increased the tendency ofreduced pressure and temperature to increase the first stage duration asignition is advanced eventually exceeds the advance and no furtherreduction in strength or increase in speed is possible.

It can be shown that the size of the opposing surfaces of conventionalelectrodes contributes to the relatively slow completion of the firststage of combustion, since the relatively large areas of metalcontribute a cooling effect on the burning mixture. Indeed it can becalculated that the duration of the first stage approximately matchesthe time for the flame front to reach the limit of the electrodes.

U.S. Pat. No. 4,465,952 discloses a spark plug in which the central andside electrodes define respective parallel, elongate sparking surfacesarranged opposite one another. The sparking surfaces are coated with anoble metal and are flanked along their longitudinal edges by oppositelyinclined surfaces sloping away from the sparking surfaces. However, sucha spark plug is expensive to produce and does not satisfactorily solvethe problem of igniting weak mixtures.

U.S. Pat. No. 4,122,816 discloses a spark plug having a centralelectrode having a frustoconical end whose outer curved surfaceconstitutes a first sparking surface, and an annular side electrodesurrounding the central electrode and having an inner surface offrustoconical shape inclined in the opposite direction to thefrustoconical end of the central electrode and defining a secondsparking surface opposite the first sparking surface. The spark gap ofsuch a spark plug is generally annular and diverges towards the end ofthe central electrode. Whilst such an arrangement of the sparkingsurfaces will tend to cause the spark to advance towards the end of thesparking surfaces during ignition, the spark will tend to be confined bythe annular shape of the side electrode. Furthermore the shape of thesparking surfaces will tend to result in wear of the surfaces inoperation resulting in uneven sparking.

In view of the foregoing it is an object of the present invention toprovide a carburetor metering system capable of accurately controllingfuel flow over a wide range of air flows and mixture strengths.

It is another object of this invention to provide a spark plug for usein a combustion system in which the effect of weak mixture on theduration of the first stage is minimized, this enabling the knownadvantages of lean mixtures to be realized, affording favorablecombustion characteristics and fuel economy as well as minimizingpollution from unburnt or incompletely burnt gases.

It is another object of the present invention to provide an improvedwick construction which provides an improved vaporization rate.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a carburetormetering system comprising a fuel valve for injecting liquid fuel into astream of air, the valve comprising a valve member movable along adisplacement axis with respect to a valve seat to vary the fuel flowthrough the valve, the valve member and the valve seat havingsubstantially parallel surfaces which are inclined with respect to thedisplacement axis and which define therebetween a passage for the flowof fuel having a width corresponding to the distance apart of thesurfaces and a length corresponding to the degree of overlap of thesurfaces, the length of the passage varying substantially in proportionto the width as the valve member is moved along the displacement axis.

The system of the invention has been developed after detailed study ofthe mechanisms which affect fuel flow rates in conventional carburetors.As is well known, a pressure difference induced by the air flow isgenerally used to drive fuel through the metering orifice, and the fuelflow rate is caused to vary in dependence on the air flow rate. However,the fuel flow rate tends to vary unpredictably with air flow rate due tothe fact that there are two different mechanisms which determine therelevant pressure differentials, one of which arises from the viscosityof the fluid and the other of which is dependent on momentum changes ofthe fluid. The relative magnitude of the two mechanisms varies withtemperature and pressure, as well as with fluid flow. Furthermore, therelative magnitude of the two mechanisms is different for fuel and airin view of the different volume flow rates of fuel and air. The systemof the invention is chosen so as to minimize the effects of momentumchanges in the fuel orifice.

In a further aspect of the invention the system further comprises an aircontrol valve for varying the air flow in dependence on movement of thevalve member of the fuel valve. Preferably the geometry of the aircontrol valve is chosen such that the effect of the viscosity of the airon the pressure difference across the valve is negligible. Furthermorethe relative geometries of the throughflow orifice of the fuel valve andthe air control valve are preferably such that, with a constant pressuredifference across the air control valve, the mixture strength issubstantially independent of flow over a wide range of air flows. Theair control valve comprises a seat member and a gate member cooperatingto define at least one triangular orifice, the gate member being movablewith respect to the seat member to vary the throughflow cross-section ofthe orifice.

The fuel valve has a circular orifice within which a tapered end of thevalve member is movable, the fuel passage being defined between afrustoconical surface of the tapered end of the valve member and asurrounding frustoconical surface of the valve seat.

Furthermore it is advantageous for the valve seat to have a cylindricalsurface which lies immediately upstream of its frustoconical surface andwhich merges steplessly into its frustoconical surface.

In addition it is advantageous for the valve member to have acylindrical surface which lies immediately downstream of itsfrustoconical surface and which merges steplessly into its frustoconicalsurface.

Also in accordance with the present invention, a wick for use acarburetor metering system is provided for absorbing liquid forvaporization into an air flow, comprising a cloth of woven strands andmeans for suspending said cloth in the air flow.

Also in accordance with the present invention there is provided a sparkplug for use in a fuel combustion system, said spark plug having acentral electrode and a side electrode having respective sparkingsurfaces arranged opposite one another and defining a spark gaptherebetween, each of the sparking surfaces being elongate and beingflanked along its longitudinal edges by oppositely inclined surfacessloping away from the sparking surface, wherein the two sparkingsurfaces are inclined relative to one another in the longitudinaldirection so that the spark gap widens in the direction in whichsparking tends to advance along the gap.

Preferably the central electrode has a circular cross-section at adistance from its sparking surface and its sparking surface constitutesan end surface of the central electrode. The sparking surface of thecentral electrode conveniently has its longitudinal edges symmetricallydisposed with respect to a diameter of the central electrode.

The side electrode is preferably elongate and extends inwardly from oneside of the central electrode and its sparking surface extends generallylengthwise of the side electrode. Preferably the sparking surface of theside electrode has its longitudinal edges symmetrically disposed withrespect to the direction in which the side electrode extends. The sideelectrode may be generally L-shaped.

In an alternative embodiment of the spark plug according to theinvention the sparking surface of the central electrode is disposed onone side of the central electrode, and the sparking surface of the sideelectrode constitutes an end surface of the side electrode which extendsinwardly from one side of the central electrode.

According to another aspect of the present invention a carburetormetering system is provided, comprising air flow control valve means,including an air inlet and an air outlet, for metering the flow of airfrom said air inlet to said air outlet in dependence upon the airpressure differential between the air inlet and air outlet to maintainthe pressure differential at a predetermined value, fuel valve meanshaving an inlet connected to a source of fuel, and an outlet, said fuelvalve means being operatively connected to said air flow control valvemeans so that the fuel valve means provides a respective increase anddecrease in fuel flow rate in respective dependence upon an increase anddecrease in air flow rate by said air flow control means, and a fuelpressure differential valve means for maintaining the pressuredifferential across the fuel valve means substantially constant, tothereby provide a metering system wherein the fuel and air pressures arecontrolled separately. Preferably, two restrictors are connected inseries across the fuel valve means at the inlet and outlet, and the fuelpressure differential valve means comprises a chamber having a diaphramto define first and second subchambers, the first subchamber being incommunication with the valve means outlet and the outlet, and the secondsubchamber being in communication with the junction of the tworestrictors, such that the pressure difference across the diaphram isfixed and is a predetermined fraction of the total pressure differenceacross the first fuel valve means.

According to another aspect of the invention, a fuel carburetor meteringsystem is provided for use in a fuel combustion engine having loadsranging from part load to full load, comprising means for vaporizingliquid fuel into an air flow at a relatively constant mixture strengthfor a full load condition, means, downstream of said means forvaporizing, for introducing hot dilution air into said air flowcontaining vaporized fuel, and means for controlling the amount of hotdilution air introduced into said air flow in response to loadconditions of said engine, to provide a relatively leaner mixture atpart load conditions and a relatively richer mixture at full loadconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-sectional view of a fuel valve of a meteringsystem according to the present invention;

FIG. 2 is a schematic diagram of a metering system for fuel and air inaccordance with the present invention;

FIG. 3 is an alternative arrangement of a metering system for fuel andair in accordance with the present invention;

FIG. 4 is a schematic diagram of an overall arrangement for a carburetormetering system according to the present invention, showing inparticular an arrangement for adding hot dilution air;

FIG. 5 is a cross-sectional view of the wick chamber of FIG. 4 ingreater detail;

FIG. 6 is a perspective view of the wick material of the wick chamber ofFIG. 5;

FIG. 6A is a cross-sectional view of a strand of six fibers from thewick material of FIG. 6:

FIG. 7 is a perspective view of the vortex chamber of FIG. 4 in greaterdetail;

FIG. 8 is a perspective view of the operative end of a spark plugaccording to the invention;

FIG. 9 is an enlarged perspective view of the electrodes of the sparkplug of FIG. 8; and

FIG. 10 is a side view of the electrodes of the spark plug of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, a carburetor metering systemis provided comprising a fuel valve for injecting liquid fuel into astream of air, the fuel valve comprising a fuel valve member movablealong a displacement axis with respect to a valve seat to vary the fuelflow through the fuel valve between twos limiting positions, namely asubstantially closed position and a fully open position, the fuel valvemember and the valve seat having substantially parallel surfaces whichare inclined with respect to the displacement axis and which definetherebetween a passage for the flow of fuel having a width correspondingto the distance apart of the surfaces and a length corresponding to thedegree of overlap of the surfaces, the form of said surfaces being suchthat, as the fuel valve member is moved along the displacement axis fromits substantially closed position towards its fully open position, thelength and the width of the passage increase substantiallyproportionally from values of substantially zero. The carburetormetering System also preferably comprises an air control valve foradjusting the fuel valve member to vary the fuel flow through the fuelvalve, in dependence on the air flow.

The geometry of the air control valve is chosen preferably such that theeffect of the viscosity of the air on the pressure difference across theair control valve is negligible. The relative geometries of thethroughflow orifice of the fuel valve and the air control valve are suchthat, with a constant pressure difference across the air control valve,the mixture strength is substantially independent of air flow over awide range of air flows.

The carburetor metering system also preferably includes wick means forabsorbing liquid fuel and for exposing said fuel to the air flow. Thewick means may be made of a cloth of woven strands wherein each of thestrands comprises a plurality of twisted or braided fibers of metalwire, glass or natural material. Preferably six fibers are provided andare arranged with one central fiber and five fibers twisted around saidcentral fiber.

Also according to the present invention, a fuel combustion system isprovided including the above described carburetor metering systemcombined with at least one spark plug. The spark plug preferably has acentral electrode and a side electrode having respective sparkingsurfaces arranged opposite one another and defining a spark gaptherebetween, each of the sparking surfaces being elongate and beingflanked along its longitudinal edges by oppositely inclined surfacessloping away from the sparking surface, wherein the two sparkingsurfaces are inclined relative to one another in the longitudinaldirection so that the spark gap widens in the direction in whichsparking tends to advance along the gap. The central electrode has acircular cross-section at a distance from its sparking surface and itssparking surface constitutes an end surface of the central electrode.The sparking surface of the central electrode has its longitudinal edgessymmetrically disposed with respect to a diameter of the centralelectrode. The side electrode is elongate and extends inwardly from oneside of the central electrode and its sparking surface extends generallylengthwise of the side electrode. The sparking surface of the sideelectrode has its longitudinal edges symmetrically disposed with respectto the direction in which the side electrode extends. The side electrodeis generally L-shaped. The sparking surface of the central electrode mayalternatively be disposed on one side of the central electrode, with thesparking surface of the side electrode constituting an end surface ofthe side electrode which extends inwardly from one side of the centralelectrode.

Further in accordance with the present invention a carburetor meteringsystem is provided, comprising air flow control valve means, includingan air inlet and an air outlet, for metering the flow of air from saidair inlet to said air outlet in dependence upon the air pressuredifferential between the air inlet and air outlet to maintain thepressure differential at a predetermined value, fuel valve means havingan inlet connected to a source of fuel, and an outlet, said fuel valvemeans being operatively connected to said air flow control valve meansso that the fuel valve means provides a respective increase and decreasein fuel flow rate in respective dependence upon an increase and decreasein air flow rate by said air flow control means, and a fuel pressuredifferential valve means for maintaining the pressure across the fuelvalve means substantially constant, to thereby provide a metering systemwherein the fuel and air pressures are controlled separately.

Preferably, two restrictors are connected in series across the fuelvalve means at the inlet and outlet, and the fuel pressure differentialvalve means preferably comprises a chamber having a diaphram to definefirst and second subchambers, the first subchamber being incommunication with the fuel valve means outlet and the second subchamberbeing in communication with the junction of the two restrictors, suchthat the pressure difference across the diaphram is fixed and is apredetermined fraction of the total pressure difference across the fuelvalve means. The restrictors are preferably adjustable. The fuel valvemeans preferably comprises a fuel valve member movable along adisplacement axis with respect to a valve seat to vary the fuel flowbetween two limiting positions, namely a substantially closed positionand a fully open position, the fuel valve member and the valve seathaving substantially parallel surfaces which are inclined with respectto the displacement axis and which define therebetween a passage for theflow of fuel having a width corresponding to the degree of overlapbetween the surfaces, the form of said surfaces being such that, as thefuel valve member is moved along the displacement axis from itssubstantially closed position towards its fully open position, thelength and width of the passage increase substantially proportionallyfrom values of substantially zero.

Wick means are also preferably provided for absorbing liquid fuel andfor exposing said fuel to the air flow. The wick means comprises a clothof woven strands, wherein each of the strands comprise a plurality oftwisted or braided fibers made of metal wire, glass, or naturalmaterial. Preferably six fibers are provided and are arranged with onecentral fiber and five fibers twisted around said center fibers.

According to another aspect of the invention, a fuel combustion systemis provided comprising the carburetor metering system just described,and including at least one spark plug, wherein said spark plug may be inthe particular form described above.

Further in accordance with the present invention, a fuel carburetormetering system for use in a fuel combustion engine having loads rangingfrom part load to full load is provided comprising means for vaporizingliquid fuel into an air flow at a relatively constant mixture strengthsuitable for a full load condition; means, down stream of said means forvaporizing, for introducing hot dilution air into said air flowcontaining vaporized fuel; and means for controlling the amount of hotdilution air introduced into said air flow in response to roadconditions of said engine, to provide a relatively leaner mixture atpart load conditions and a relatively richer mixture at full loadconditions. The fuel carburetor metering system further includesthermostatic valve means for introducing hot dilution air into said airflow only in response to the dilution air being greater than apredetermined temperature. The means for introducing hot dilution airpreferably comprises a vortex chamber for introducing the hot dilutiontangentially and transverse to the air flow containing vaporized fuel.The metering system further includes a heat exchanger for heating air toprovide the hot dilution air, and an air intake port, and wherein theheat exchanger and the means for vaporizing liquid fuel are bothconnected to receive air from the air intake port.

Further in accordance with the present invention, a wick for use in acarburetor metering system is provided for absorbing liquid fuel forvaporization into an air flow. The wick may be in the form as describedabove.

Further in accordance to the present invention, a method for meteringliquid fuel and air for carburetion is provided comprising metering theflow of air between an air inlet and an air outlet in an air controlvalve in dependence upon the air pressure differential across the valveto maintain the pressure differential at a predetermined value, meteringa source of the liquid fuel from a fuel inlet to a fuel outlet independence of the metering of the flow of air so that the liquid fuelmetering respectively increases and decreases when the air flow rateincreases and decreases, and maintaining the pressure across the firstfuel valve means substantially constant, whereby the fuel and airpressures are controlled separately.

Further in accordance with the present invention, a method for meteringfuel is provided for use in a fuel combustion engine having loadsranging from part load to full load, comprising vaporizing liquid fuelinto an air flow at a relatively constant mixture strength suitable fora full load condition, introducing hot dilution air into the air flowhaving the vaporized fuel, and controlling the amount of hot dilutionair introduced into said air flow in response to load conditions of saidengine, to provide a relatively leaner mixture at part load conditionsand a relatively richer mixture at full load conditions.

Refering to FIG. 1, the fuel valve 10 comprises a needle valve member 12movable along a displacement axis 13 with respect to a valve seat 14.The valve 10 has a circular orifice 15 by way of which liquid fuel isinjected into a stream of air. The valve member 12 has an outercylindrical surface 16 and a tapered end defining a frustoconicalsurface 17. The valve seat 14 has an inner cylindrical surface 18 and afrustoconical surface 19 surrounding the frustoconical surface 17 of thevalve member 12. The valve seat 14 is provided with a fuel inlet 20.

The conical angle of the frustoconical surface 17 matches the conicalangle of the frustoconical surface 19, and the two surfaces 17 and 19overlap one another so as to define therebetween an annular passage forthe flow of fuel. It will be appreciated that the length of overlap L ofthe surfaces 17 and 19 will vary substantially in proportion to thewidth W of the passage as the valve member 12 is moved along thedisplacement axis 13 with respect to the valve seat 14. Thus the fuelflow through the orifice 15 for a given pressure difference isproportional to the square of the width W which is in turn proportionalto the degree to which the valve member 12 is lifted.

FIG. 2 shows the fuel valve 10 connected to a conventional float chamber21 for supplying liquid fuel to the valve 10. The fuel orifice 15 opensinto an air duct 22 provided with a throttle 23. The valve member 12 isconnected to a movable diaphragm 24 capable of being deflected in thedirection of the arrows 25 to move the valve member 12 with respect tothe valve seat 14 so as to vary the fuel flow through the valve 10. Alsoconnected to the diaphragm 24 is a gate member 26 of an air controlvalve 27. The gate member 26 has a cylindrical wall having a pluralityof triangular cut-outs 28 along its edge. Furthermore the gate member 26fits within the cylindrical end of the duct 22 which defines a seatmember 29 of the air control valve 27.

It will be appreciated that, as the diaphragm 24 is deflected in thedirection of the arrows 25, the gate member 26 will be moved within theseat member 29 so as to vary the throughflow cross-section of thetriangular cut-outs 28. Thus the throughflow cross-section of the aircontrol valve 27 varies in proportion to the square of the degree ofdeflecting of the diaphragm 24, and hence the degree of displacement ofthe valve member 12.

The geometries of the orifices of the fuel valve 10 and the air controlvalve 27 are chosen so as to ensure that, with a constant pressuredifference across the air control valve, the mixture strength isindependent of flow over a range limited only by manufacturinginaccuracy, and so that adjustment of the pressure difference can beused to adjust the mixture strength. In this regard the pressuredifference across the air control valve 27 is used to effect lifting ofthe gate member 26.

With this arrangement the mixture strength is proportional to the squareroot of the pressure difference. If required the mixture strength can beadjusted by arranging for only an adjustable fraction of the wholepressure difference across the air control valve 27 to be used to liftthe gate member 26 against its dead weight or a return spring.Typically, it is necessary to adjust the pressure difference to providevariable mixture strength and compensate for changes in fuel viscosityand air density.

It will be appreciated that the particular geometries of the valvemember 12 and the valve seat 14 of the fuel valve 10 are advantageousbecause they ensure that pressure differences related to the viscosityof the fuel are substantially greater than pressure differences due tomomentum changes of the fuel, and since the essential geometry of thefuel passage is maintained as the throughflow cross-section is varied.

The described carburetor metering system is capable of accuratelycontrolling the fuel flow over a wide range of air flows and mixturestrengths, and is therefore particularly applicable to lean mixtureoperation. The system typically has a response time of the order of atenth of a second.

FIG. 3 shows another embodiment of a carburetor metering systemaccording to the invention. In this system, the fuel metering valve ismechanically connected to the air valve.

In FIG. 3, a carburetor metering system 30 is shown wherein liquid fuelfrom a fuel pump (not shown) enters a fuel inlet 31 of a fuel valve 32.The fuel valve 32 has an outlet 33 connected to a fuel chamber 34arranged as a pressure differential chamber as will be described. Thefuel valve 32 may be arranged in the geometry according to FIG. 1 exceptthat the exit is not exposed to the air. The fuel valve 32 has a valvemember 35 mechanically connected and operatively coupled to an air valvemember 36.

The air valve member 36, shown schematically, is arranged as an invertedcup and has triangular cut-outs 37 arranged around its periphery. Theinverted cup is received in a seat 38 having an annular chamber 39connected to an air outlet 40. A pressure link 41 connects the airoutlet 40 and the upper interior region 42 of the seat 38 to maintainthe region 42 at equal pressure with air outlet 40. As is apparent fromthe air valve shown and described, the valve member moves upwardly wheninlet air pressure exceeds air outlet pressure present in air outlet 40and upper region 42. As the air valve member 36 moves verticallyupwardly, a greater portion of the triangular regions 37 will intersectthe annular chamber 39, thus increasing air flow through the air valve.When outlet pressure decreases relative to inlet pressure, valve member36 drops, thus decreasing air flow through the air valve. Movement ofthe valve member 36 vertically will cause the fuel valve member to movelikewise due to mechanical coupling 43.

The fuel chamber 34 has an upper subchamber 34a and a lower subchamber34b, separated by a diaphragm 44. The diaphragm 44 is flexibly mountedin the vertical center of the chamber as shown. Mounted on the diaphragm44 is a fuel valve 45 which is received in fuel outlet seat 46 ofchamber 34. A spring 47 is also provided between diaphragm 44 and thetop of the chamber 34.

The lower subchamber 34b is connected to the junction point of twoadjustable restrictors 48 and 49 connected in series across the fuelinlet 31 and fuel outlet 33 of fuel valve 32. The pressure differencebetween subchamber 34a and 34b is a fraction of the total pressure dropacross the fuel valve 32, the fraction being determined by the settingof the adjustable restrictors 48 and 49.

In operation, excess fuel flow through fuel valve 32 for a givenposition of fuel valve member 35 (and in turn a given position of airvalve member 36 and hence given air flow) causes fuel valve 45 to movevertically upwards towards a more closed position, due to drop inpressure in subchamber 34a relative to subchamber 34b, and hencecorrects fuel flow excess. The spring force from spring 47 issubstantially constant since air pressure drop to lift air valve member36 is constant. A fuel drain 50 disposes of leakage fuel, which, sinceit is relatively small in quantity, can be added to air flow since fuelhas already passed metering fuel valve 35.

Restrictors 48 and 49 control the air/fuel mixture strength. Either oneof these restrictors can be fixed. Both of these restrictors allow onlya relatively small flow compared to fuel valve 32. Any flow throughrestrictors bypasses metering fuel valve 35 and no flow enters or leavessubchamber 34b except in transients.

The best arrangement for metering and mixture monitoring is to operatethe basic system at a constant mixture strength, because thermometerswhich are used to measure temperature drop (across an evaporator forexample) do not respond quickly enough to changes. However, dutyrequires a lean fuel mixture at part load, and a richer full strengthmixture at full load.

At part load it is advantageous to reduce the weight of charge taken byengine. Reducing the charge by using throttling is not desirable becauseit lowers intake manifold pressure, needing more work from engine andcausing back flow of exhaust. One can advantageously heat the air/fuelcharge with waste heat to reduce density and hence the weight withoutchange (or substantial change) of pressure. Heating has to be rapid tocover transients.

FIG. 4 is a schematic showing an overall arrangement for a carburetormetering system according to the invention in the environment of avehicle, for example, and shows in particular an arrangement accordingto the invention for adding hot dilution air. The schematic layout showsan air cleaner 55 providing air to an air valve 56 connected in turn toa mixture throttle 57. The mixture throttle 57 is connected to a fuelwick chamber 58 having a wick 59, which will be described in more detailbelow. The wick chamber 58 functions as an evaporator for the liquidfuel. The vaporized fuel/air mixture then goes to a vortex chamber 60,to be described in more detail below, and then to an intake manifold 61.

Also shown in FIG. 4 is an air path on the left, wherein air from aircleaner 55 is provided to a diluent throttle 62. The diluent throttle 62is controlled by cam 63 whereas the mixture throttle 57 is controlled bycam 64, and both cams are controlled by the same camshaft turned by theaccelerator pedal of a vehicle. The shapes of the cams would bedetermined by engine testing.

The output from the diluent throttle 62 is connected to a heat exchanger65, which may be physically located adjacent an existing heat sourcesuch as an exhaust manifold or exhaust pipe. The heat exchanger 65 isconnected to a thermostatic valve 66 and then to the vortex chamber aswill be described below.

The arrangement shown in FIG. 4 according to the invention providesdilution air downstream of an evaporator wick system. In thisarrangement, since wick exit flow and diluent are both gas, the properproportion is not difficult to arrange or maintain. The presentinvention provides for using hot dilution air with the added advantagethat raising inlet temperature extends lean burn range. The precisetemperature can be determined experimentally and is achievable. Dilutionfrom a reservoir of hot air provides very fast transient response.

In FIG. 4, diluent air is extracted from the air cleaner 55, passedthrough its own throttle 62, through a heat exchanger and finally to asecond valve 66 to a vortex chamber 60. The diluent throttle 62 has thesame temperature at entry as does the main mixture throttle 57, tomaintain flow balance. The second (thermostatic) valve 66 is controlledby a temperature sensor and is closed when the air is cold, so that nodilution is provided when the air is cold.

While FIG. 4 shows the mixture throttle 57 upwind of the wick chamber58, it may be downwind. Experimental results will very well dictatewhich is the preferred arrangement if any.

FIG. 5 shows the wick chamber 58 of FIG. 4 in greater detail. The wickchamber 58 may take many forms, including those shown in U.S. Pat. No.4,290,401 for example, which is incorporated by reference herein. InFIG. 5 the wick chamber includes an upper conical container portion 70aand a lower conical container portion 70b and having an air inlet 71 anda vapor mix outlet 72. A wick support grid 73, which may be in the formof a wire screen or mesh of a coarser size then the wick, is provided tosupport a wick 59 in a pyramid fashion as shown. Liquid fuel is shownschematically injected into the wick chamber 58, and can be injected bysprinkling or spraying means to spread the fuel out over the wick.

The wick 59 may be in the form of a closely woven cloth of spun fibersas shown in FIG. 6. The strands in the weave of cloth contain 6 (six)fibers which are spun or twisted in a conventional manner. Liquid fuelinjected into the wick chamber 58 will spread by capillary action andlodge in the fine spaces between the fibers and will evaporate into theair as the air streams through the cloth as shown in FIG. 6A. The fiberdiameter should preferably be as small as possible within theconstraints of material strength and availability. A drain 74 isprovided for the run-off of unevaporated liquid fuel. Since fuelinjected into the wick chamber has already been metered, the drain 74 isnot necessary, and liquid fuel can be allowed to run out of the vapormix outlet 72. The drain 74 may be connected further downstream of thewick chamber 58.

The small size of the fiber gives maximum surface area for a givenweight of fuel resident and lodged in the structure. The small size alsogives maximum evaporation effect for given pressure drop in airways.While it is possible to use more than one layer of wick of coarser size,a single fine layer is preferred.

The fibers of the wick may be composed of spun long fibers of wire,glass or natural material. As stated above, an arrangement of six fibersto comprise one strand is the preferred construction in terms of surfacearea, fuel spreading along the spaces between the fibers within thestrands, minimum resident fuel, i.e. quantity of fuel needed to wet thewick surface, and exposure to air flowing in the fine air spaces betweenthe fibers. Of the three materials of wire, glass or natural material,the wire can act as a flame trap and has minimal risk of sheddingfragments into the airstream. It is therefore preferred and the effectsof heat spread through the metal is probably, on balance, an advantage.

Referring again to FIG. 5, under cold conditions, a fraction of the fuelwill likely fail to evaporate in the cold air passing the wick. Thesimplest means of disposal is to use a small additional wick in thediluent air stream. The run off is passed to this wick where it joinsthe main flow as vapor.

Referring now to FIG. 7, the vortex chamber 60 of FIG. 4 is shown ingreater detail. The vortex chamber 60 has an inlet 80 which receivesair/fuel mixture from the wick chamber and an outlet 81 which isconnected to the intake manifold for the engine. Hot diluent air fromthermostatic valve 66 is provided at side inlet 82 into an enlargedannular vortex mixing chamber 83. The hot diluent air is providedtangentially to the annular chamber and transverse to the air/fuelmixture flow, where the hot diluent air follows a circular helical path.Mixing of the hot diluent air with the cold air in the generallydownward vertical direction is encouraged by the fact that the moredense cold air mixture will try to move radially outwards while the hot,less dense diluent air will try to move inwardly.

A spark plug according to one aspect of the present invention will nowbe described with reference to FIGS. 8-10. The illustrated spark plug isof generally conventional construction except for the electrodes, aswill be described. The spark plug as shown in FIG. 8 has a body 85 ofconventional form including an externally screw-threaded portion 86 anda hexagonal or other portion by means of which it can be engaged by aspanner or socket to fit or remove it from an engine cylinder head orequivalent part.

Within the body 85 is a ceramic insulator 12 which is positioned withinthe screw-threaded hollow cylindrical end of the body 85. There is a gaparound the insulator 87 and its shape may be determined in a knownmanner dictated by cooling or other factors.

Passing through the center of the insulator 87 is a central electrode88. This extends right through the insulator and terminates in ascrew-threaded portion or other portion to which a lead can beconnected.

Fixed, as by welding, to the annular end of the body 85 is a side orearth electrode 89. This is of L-shape having one limb secured to thebody 85 and the other limb extending over the central electrode 88.

As seen particularly in FIG. 9 the central electrode 88 is ofcylindrical form but its end is shaped to provide a flat narrowrectangular rail-like surface 90 flanked by two inclined surfaces 91,92.

The side electrode 89 has a surface presented towards the centralelectrode, this surface being shaped to provide a narrow rail-likesurface 93 aligned with the surface 90 on the central electrode and ofgenerally the same proportions. The surface 93 on the side electrode 89is also flanked by inclined surfaces 94, 95. The portion of the surface90 on the central electrode is parallel sided and of similar width andlength to the surface 90 on the central electrode but is then flared soas to merge with the surface of the side electrode as shown.

The inclined surfaces 91, 92, 94, 95 provide substantial clearancebetween the electrodes other than in the regions of the opposingsurfaces 90 and 93.

As seen in FIG. 10 the surfaces 90 and 93 lie at a small acute anglerelative to one another with the narrowest gap between them being at theend at which the side electrode 89 is secured to the body 85 of thespark plug.

In use the spark plug is fitted into a combustion chamber of an internalcombustion engine in conventional manner and means are provided forapplying a high voltage current across the gap between the twoelectrodes to create a spark. Spark initiation occurs at the point atwhich the two surfaces 90 and 93 are closest together, that is, at theend towards the junction of the side electrode with the spark plug body.The magnetic forces produced by the current in the spark and the sideelectrode causes the spark to travel along the rail-like surfaces 90, 93towards the free end of the side electrode.

The translation of the arc along the rail-like surfaces will have theeffect of supplying heat to and hence igniting a larger quantity ofmixture than if the spark were static. This cools the thread of gaswhich is conducting the electrical current. This increases itselectrical resistance and since external resistance, due to the leadsand the coil, or its equivalent, is largely fixed, there will tend to bean increase in electrical energy at the arc.

Furthermore, the substantial clearance at either side of the rail-likesurfaces 90, 93 enables the flame front to grow in area as it advances,thus rapidly reaching a larger volume of fresh combustible mixture.Cooling effects of the bodies of metal represented by the electrodes arealso minimized.

The translation of the arc, extra arc energy, better exposure ofcombustible mixture and minimized cooling all contribute to a reductionof the duration of the first stage of ignition, the greater reductionoccurring under the more difficult case of leaner mixture.

It might be supposed that the large area of the conventional electrodeshas the effect of prolonging the life of the spark plug. However,erosion of the electrodes is governed by the amount of heat reaching anyparticular volume of metal. When, as here described, the arc isdeliberately caused to traverse the rail-like surfaces, the amount ofheat to any particular volume is minimized with ensuing prolongation ofthe electrode life.

The spark plug as described therefore provides a high efficiency sparkinitiation and flame generation pattern giving good combustioncharacteristics and also enabling lean mixtures to be effectively used,thus enhancing the fuel economy of the engine. Good combustioncharacteristics also ensure maximum burning of the mixture in thecombustion chamber so that exhaust pollution is minimized.

The spark plug according to the invention can also have different typesof electrodes. For example, the side electrode may extend laterallydirectly towards the side of the central electrode from the adjacentwall of the body, either at a level with the end of the body or aboveit.

Although preferred embodiments of the invention have been disclosed anddescribed herein, it should be understood that the present invention isin no sense limited thereby and its scope is to be determined only bythat of the appended claims.

I claim:
 1. A carburetor metering system, comprising:air flow controlvalve means, including an air inlet and an air outlet, for metering theflow of air from said air inlet to said air outlet in dependence uponthe air pressure differential between the air inlet and air outlet tomaintain the pressure differential at a predetermined value; fuel valvemeans having an inlet connected to a source of fuel, and an outlet, saidfuel valve means being operatively connected to said air flow controlvalve means so that the fuel valve means provides a respective increaseand decrease in fuel flow rate in respective dependence upon an increaseand decrease in air flow rate by said air flow control means; a fuelpressure differential valve means for maintaining the pressuredifferential across the fuel valve means substantially constant, saidfuel pressure differential means comprises a chamber having a diaphragmto define first and second subchambers; and restricter means connectedacross the fuel valve means at the inlet and outlet, wherein thepressure across the diaphragm is at a fixed predetermined fraction ofthe total pressure difference across the fuel valve means, to therebyprovide a metering system wherein the fuel and air pressures arecontrolled separately.
 2. A carburetor metering system according toclaim 1, wherein the restricter means comprises two restrictorsconnected in series across the fuel valve means at the inlet and outlet,and wherein the fuel pressure differential valve means comprises achamber having a diaphragm to define first and second subchambers, thefirst subchamber being in communication with the fuel valve means outletand the second subchamber being in communication with the junction ofthe two restrictors.
 3. A carburetor metering system according to claim2, wherein the two restrictors are adjustable.
 4. A carburetor meteringsystem according to claim 1, wherein the fuel valve means comprises afuel valve member movable along a displacement axis with respect to avalve seat to vary the fuel flow between two limiting positions, namelya substantially closed position and a fully open position, the fuelvalve member and the valve seat having substantially closed position anda fully open position, the fuel valve member and the valve seat havingsubstantially parallel surfaces which are inclined with respect to thedisplacement axis and which define therebetween a passage for the flowof fuel having a width corresponding to distance apart of the parallelsurfaces and a length corresponding to the degree of overlap between theparallel surfaces, the form of said surfaces being such that, as thefuel valve member is moved along the displacement axis from itssubstantially closed position towards its fully open position, thelength and width of the passage increase substantially proportionallyfrom values of substantially zero.
 5. A carburetor metering systemaccording to claim 1, further including wick means for absorbing liquidfuel and for exposing said fuel to the air flow.
 6. A carburetormetering system according to claim 5, wherein the wick means comprises acloth of woven strands.
 7. A carburetor metering system according toclaim 6, wherein each of the strands comprises a plurality of twisted orbraided fibers.
 8. A carburetor metering system according to claim 7,wherein the fibers are made of metal wire.
 9. A carburetor meteringsystem according to claim 7, wherein the fibers are made of glass.
 10. Acarburetor metering system according to claim 7, wherein the fibers aremade of natural material.
 11. A carburetor metering system according toclaim 7, wherein the plurality is six and the fibers are arranged withone central fiber and five fibers twisted around said central fiber. 12.A carburetor metering system according to claim 1, adapted for use in afuel combustion system, said system including at least one spark plug.13. A carburetor metering system according to claim 12, wherein saidspark plug has a central electrode and a side electrode havingrespective sparking surfaces arranged opposite one another and defininga spark gap therebetween, each of the sparking surfaces being elongateand being flanked along its longitudinal edges by oppositely inclinedsurfaces sloping away from the sparking surface, wherein the twosparking surfaces are inclined relative to one another in thelongitudinal direction so that the spark gap widens in the direction inwhich sparking tends to advance along the gap.
 14. A carburetor meteringsystem according to claim 13, wherein the sparking surface of thecentral electrode has a circular cross-section at a distance from itssparking surface and its sparking surface constitutes an end surface ofthe central electrode.
 15. A carburetor metering system according toclaim 14, wherein the sparking surface of the central electrode has itslongitudinal edges symmetrically disposed with respect to a diameter ofthe central electrode.
 16. A carburetor metering system according toclaim 13, wherein the side electrode is elongate and extends inwardlyfrom one side of the central electrode and its sparking surface extendsgenerally lengthwise of the side electrode.
 17. A carburetor meteringsystem according to claim 16, wherein the sparking surface of the sideelectrode has its longitudinal edges symmetrically disposed with respectto the direction in which the side electrode extends.
 18. A carburetormetering system according to claim 16, in which the side electrode isgenerally L-shaped.
 19. A carburetor metering system according to claim13, wherein the sparking surface of the central electrode, and thesparking surface of the side electrode constitutes an end surface of theside electrode which extends inwardly from one side of the centralelectrode.
 20. A method for metering liquid fuel and air forcarburetion, comprising:metering the flow of air between an air inletand an air outlet in an air control valve in dependence upon the airpressure differential across the air control valve to maintain thepressure differential at a predetermined value, metering a source ofliquid fuel from a fuel inlet to a fuel outlet in dependence on themetering of the flow of air so that the liquid fuel meteringrespectively increases and decreases when the air flow rate increasesand decreases, maintaining the pressure across a fuel pressuredifferential valve means at a substantially constant first pressurevalue and maintaining the pressure across a fuel valve means at apredetermined second pressure value, said first pressure value being afixed fraction of said first pressure value, whereby the fuel and airpressures are controlled separately.